Working with the cinematographers Guy Mossman and Luke Geissbühler, and shooting in digital that I often wished were film (the big-sky landscapes deserve a more nuanced texture), she tags after Mr. Brannaman, well, kind of as his trained horses do. That isn’t a bad thing. He and all the pretty horses make for mesmerizing viewing, especially when he’s quieting colts (he calls them babies) and their often more jittery handlers. “A lot of times,” he says in the voice-over that opens the movie, “rather than helping people with horse problems, I’m helping horses with people problems.”

Sometimes they’re the same thing, as a violent interlude with a weepy woman and her seemingly crazed stallion proves. This part of the movie works like a punch to the gut, but, given how close it edges into hagiography, it’s also necessary as a reminder of what’s really at stake. “Buck” is an imperfect documentary. It leaves nagging questions unanswered, including the fate of Mr. Brannaman’s brother, and the movie’s beauty shots at times threaten to embalm nature instead of exalting it. Yet in some sense it was beauty that saved Mr. Brannaman, that of his conscience and that of horses, which, having been tied to humans long ago, became companions, workers and for some, as this lovely movie shows, saviors.